There are basically four possible alternatives to toxic and polluting organic solvents, according to leading green chemist Professor Ken Seddon at Queen's University Belfast, UK. The first and least practicable is not to use a solvent at all. Water is another option, though the disposal of used, polluted water is tightly controlled. "In fact, if you took water out of a river and didn't do anything with it, you wouldn't be able to return it because the level of pollution in a river is greater than the amount you are allowed to put in," Seddon says.

A third possibility, supercritical fluids such as carbon dioxide, are finding an increasing number of uses as solvents (see The distant grass is greener). The final green alternative is ionic liquids. "The first three tools are well explored," Seddon says, "but the fourth isn't."

Ionic liquids are usually associated with high-temperature processes: the extraction of aluminium from bauxite for example. This is because ionic substances like common salt are made of two very small ions with opposite electrical charges (sodium and chloride in salt's case). The similar shape and small size of these ions makes the electrical attraction between them so strong that it requires an enormous amount of energy to break the ionic bond -- common salt melts at around 800 degrees Celsius.

Obviously high-temperature 'molten salts' are unsuitable solvents for heat-sensitive organic molecules. But their melting point can be reduced -- by making ionic liquids from bulky, asymmetrical ions that only loosely fit together. And because less of the ill-fitting ions' attractive forces are used to bind neighbours, the rest can attract (and so dissolve) other compounds.

Ionic liquids could make ideal green solvents. They have negligible vapour pressure, so they do not evaporate and escape into the atmosphere and are also recyclable. They are true 'designer solvents' -- different combinations of ions make up solutions that dissolve an enormous spectrum of substances including coal, plastics, many metals and even some rocks. "You can absolutely tune your solvent to the best chemistry," Seddon says.

But low-temperature ionic fluids are very new and remain a mystery to even experienced organic chemists and chemical engineers. Compared to the 300 organic solvents widely used in the chemical industry, there are over a trillion possible ionic liquids and little or no data about even basic physical properties such as density and melting point.

Seddon aims to change that and provide process engineers with enough information about ionic liquids to make them a realistic replacement for organic solvents. To this end he heads an unusual consortium of academics and industrial representatives called QUILL, the Queen's University Ionic Liquid Laboratories.

The consortium is unusual in that the seventeen companies involved share commercial secrets. Rather than competing to develop rival ionic liquids systems, they collaborate and pool any patented technology produced. Member companies (who include some of the biggest names in the industry, such as Merck, DuPont and ICI) each pay £20,000 annually to join the club, which meets every six months to assess progress and vote on new research directions. Formed in April 1999, QUILL has already applied for patents on a series of ionic liquid systems, which each company will then adapt for its own specific requirements.

The collaboration grew from similar, yet totally separate, ionic liquid projects that Seddon was working on for individual companies. There were enormous synergies between the different ventures, yet confidentiality agreements prevented useful knowledge gained on one process being applied to a different company's system. "It was incredibly frustrating," Seddon says. Many meetings and torturous contractual negotiations later, QUILL was born.

Such sharing of commercial secrets in an academic collaboration is not unique -- the United States has over fifty similar centres -- but it is rarer to find partnerships in an area as competitive as ionic liquids. Seddon says that the lack of fundamental knowledge is what makes this collaboration possible; once the groundwork is complete, companies may decide to go their separate ways. But there's still some way to go. One QUILL researcher, excused collaborative research duties, is working through different ionic fluids, aiming for one patent application a month. With over a trillion fluids to go, he may yet need some help.